What is the difference between deep merging and shallow merging in PHP array merging?

There are two ways to merge arrays in PHP: deep merging and shallow merging. Deep merge recursively traverses the array, merges scalar values ​​and performs a deep merge of the array. Shallow merging only copies the array element by element, with subsequent array values ​​overwriting previous values, and the array as a whole being copied into the result.

Deep Merging and Shallow Merging PHP Arrays

Introduction

In PHP, there are two main Methods can merge arrays: deep merge and shallow merge. The difference between these merge behaviors is important when working with complex or nested data structures.

Deep merge

Deep merge recursively traverses the two arrays and merges each element using the following rules:

• Scalar values ​​(numbers, strings, booleans): Values ​​located later in the array overwrite earlier values.
• Array: The same keys in the two arrays will be deeply merged to create a new array. Different keys will be appended to the final result.

Shallow merge

Unlike deep merge, shallow merge will only copy two arrays element by element. Here are the differences:

• Scalar values: Same as deep merging, later values ​​overwrite previous ones.
• Array: Copy the array as a whole into the final result. This means that if two arrays have the same keys, the latter array will overwrite the keys of the previous array.

Practical Case

The following example demonstrates the difference between deep merging and shallow merging:

// 深度合并
$array1 = ['foo' => 'bar', 'nested' => ['a' => 1]];
$array2 = ['foo' => 'baz', 'nested' => ['b' => 2, 'a' => 3]];
$mergedArray1 = array_merge_recursive($array1, $array2);

// 浅层合并
$array3 = ['foo' => 'bar', 'nested' => ['a' => 1]];
$array4 = ['foo' => 'baz', 'nested' => ['b' => 2]];
$mergedArray2 = array_merge($array3, $array4);

var_dump($mergedArray1); // 结果：['foo' => 'baz', 'nested' => ['a' => 3, 'b' => 2]]
var_dump($mergedArray2); // 结果：['foo' => 'baz', 'nested' => ['b' => 2]]

Conclusion

Deep merging is used to merge complex or nested data structures, while shallow merging is used to merge arrays element by element. It is important to understand the differences between these two merging methods to ensure that you are using the correct method to process your data.

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